Graphics processors and graphics processing method that allow an entire group of fragments corresponding to a patch of a render output to be culled at the patch level

Abstract

When performing tile-based rendering a first, pre-pass operation in which primitives for a tile are processed to determine visibility information, the visibility information being usable to determine whether fragments for a primitive in the sequence of primitives should subsequently be processed further for the render output, is performed. Thereafter a second, main pass operation is performed in which the further processing of fragments for primitives that were processed during the first, pre-pass operation is controlled based on the determined visibility information for the sequence of primitives, such that for fragments for which the visibility information indicates that the fragments should not be processed further for the render output some or all of the processing during the second, main pass is omitted. The visibility information indicates which primitives should be rendered for which sampling positions of the render output in a hierarchical manner.